To select lessons that require less than one day, click the checkbox next to "Part of a Lesson".

Be sure to notice that the topics you selected previously are still active. (Look at the bottom left corner of the screen to see a list of current search criteria.) When you select "Part of a Lesson", you’ll narrow your search to problems that meet all your criteria: they will be associated with the topics you’ve selected, AND they’ll require part of a lesson to complete.